1. Field of the Invention
This invention concerns a semiconductor disk apparatus (hereinafter xe2x80x9cdisk cardxe2x80x9d) used, for example, for expanding the peripheral functions of a personal computer.
2. Description of Related Art
Disk cards are used, for example, as auxiliary memory media for personal computers. A disk card has EEPROMs (electrically erasable programmable read only memories) mounted on it, in which EEPROMs are stored data in the form of files. By EEPROM herein is meant an electrically erasable and writable nonvolatile memory such, for example, as a flash memory.
A disk card sends and receives file data to and from the personal computer processor via a common bus. Integrated circuits are accommodated on the disk card, together with multiple EEPROMs, for distinguishing between file data read and write operations, and for performing file data write control and read control.
The integrated circuits are provided internally with an oscillator circuit. This oscillator circuit supplies the circuit clocks in the integrated circuits with a clock signal having a frequency of, for example, 80 MHz.
In conventional disk cards, the frequency of the clock signal generated in the oscillator circuit is set irrespective of the data transfer rate between the card and the personal computer. For this reason, when the data transfer rate is slow, the disk card operates at a clock frequency that is faster than necessary. The higher the clock frequency, the more electric power is consumed by the disk card. Conversely, when the clock frequency is made low in order to reduce power consumption, the speed of disk card operation is slowed down so that it can no longer keep up with the data transfers from the personal computer.
Also, in cases where a plurality of EEPROMs provided on the disk card perform write operations simultaneously, the current supplied to the disk card from the personal computer power supply becomes very large. Accordingly, when the capacity of the personal computer power supply is limited, for example, the number of EEPROMs mounted on one disk card must be limited also, making it impossible to provide large memory capacity on the disk card.
An object of the present invention is to provide a semiconductor disk apparatus wherewith power consumption can be reduced without lowering the data transfer rate.
To that end, the semiconductor disk apparatus to which the present invention pertains comprises: memory means for storing data; transfer means for transferring data input from the outside to the memory means and transferring data read from the memory means to the outside; oscillator means for generating a clock signal at a fixed frequency; and operating clock supply means for dividing the frequency of the clock signal according to the transfer rate of the transfer means and supplying that clock signal to the transfer means.
By altering the operating clock frequency according to the data transfer rate, it is possible to reduce the power consumption of the integrated circuitry configuring the semiconductor disk apparatus.